Publication

Influence of a lossy ground on lightning-induced voltages on overhead lines

Michel Ianoz
1996
Article
Résumé

A comprehensive study on the effect of a lossy ground on the induced voltages on overhead power lines by a nearby lightning strike is presented. The ground conductivity plays a role in both the evaluation of the lightning radiated fields and of the line parameters. To be calculated by means of a rigorous theory, both fields and line constants need important computation time, which, for the problem of interest, is still prohibitive. The aim of this paper is to discuss and analyze the various simplified approaches and techniques that have been proposed for the calculation of the fields and the line constants when the ground cannot be assumed as a perfectly conducting plane. Regarding the radiated electromagnetic field, it is shown that the horizontal electric field, the component which is most affected by the ground finite conductivity, can be calculated in an accurate way using the Cooray-Rubinstein simplified formula. The presence of an imperfectly conducting ground is included in the coupling equations by means of two additional terms: the longitudinal ground impedance and the transverse ground admittance, which are both frequency-dependent. The latter can generally be neglected for typical overhead lines, due to its small contribution to the overall transverse admittance of the line. Regarding the ground impedance, a comparison between several simplified expressions used in the literature is presented and the validity limits of these expressions are established. It is also shown that for typical overhead lines the wire impedance can be neglected as regard to the ground impedance

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Concepts associés (33)
Overhead power line
An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy across long distances. It consists of one or more uninsulated electrical cables (commonly multiples of three for three-phase power) suspended by towers or poles. Since most of the insulation is provided by the surrounding air, overhead power lines are generally the least costly method of power transmission for large quantities of electric energy.
Caténaire
Une caténaire est un ensemble de câbles porteurs et de fils conducteurs destinés à l’alimentation des moyens de transports électriques à captage du courant par dispositif aérien. Les câbles porteurs sont en cuivre, en bronze ou en aluminium-acier, quant aux fils conducteurs, ils sont en cuivre pur à 98 %, ou en cuivre allié à l'étain, au magnésium ou au cadmium. La caténaire permet de faire circuler la plupart des trains et des trams, mais aussi les trolleybus.
Ligne de transmission
Une ligne de transmission est un ensemble de deux conducteurs acheminant de concert un signal électrique, d'une source (ou émetteur) vers une charge (ou récepteur). On doit considérer une paire de conducteurs comme une ligne de transmission chaque fois que sa longueur est du même ordre de grandeur, ou plus, que la longueur d'onde de la fréquence la plus élevée du signal à transmettre. La charge étant connectée à l'extrémité de la ligne, la ligne permet de retrouver, sur son entrée, à son autre extrémité, la même résistance que la charge, cela quelle que soit la longueur de la ligne.
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